pro 3800 jaggies
Print head alignment is the first step.
Joe is right about using 360ppi because with Epsons, the image ppi needs to directly relate to the printer output in whole number conversions.
Thus 1440dpi on tyhe print output means if the image file is 360ppi, the relationship is exactly 4X, which printer and computer can use as a direct relationship. 300ppi is no - it will print but takes longer and is definitley not the way to get the finest quality output. I tested this aspect about 8 years ago and kept checking each year to continue confirmation.
It is possible that you are not seeing the jpeg jaggies (??? is that the file format???) onscreen - especially if you use a TFT rather than a CRT display.
The photograph isolates and perpetuates a moment of time: an important and revealing moment, or an unimportant and meaningless one, depending upon the photographer's understanding of his subject and mastery of his process. -Edward Weston